1. Field of the Invention
The present invention relates generally to magnetic disk drives (disk drives), and more particularly to a disk drive with an improved characterization segment pattern that reduces the test time associated with multiple profile scans used to determine reader and writer magnetic widths, and to a method of recording such pattern.
2. Description of the Related Art
This application is directed to a disk drive 10 like that exemplified by FIG. 1. As shown, a conventional disk drive 10 has a head disk assembly (HDA) 20 housed within an enclosure formed from a base 21 and a cover 24. The HDA 20 includes at least one disk 23, a spindle motor 22 for rapidly rotating the disk 23, and a head stack assembly (HSA) 40 that includes an actuator assembly 50 and a head gimbal assembly (HGA) (not numbered) with a transducer head 80 for reading and writing data. The HSA 40 is part of a servo control system that positions the transducer head 80 over a particular track on the disk to read or write information from that track. The HSA 40 earns its name from the fact that it generally includes a plurality of HGAs that collectively provide a vertical arrangement of heads called a xe2x80x9chead stackxe2x80x9d.
The industry presently prefers a xe2x80x9crotaryxe2x80x9d or xe2x80x9cswing-typexe2x80x9d actuator assembly 50 that conventionally comprises an actuator body 51 which rotates on a pivot assembly between limited positions, a coil 52 that extends from one side of the actuator body to interact with a pair of permanent magnets 60 to form a voice coil motor (VCM), and an actuator arm 54 that extends from the opposite side of the actuator body to support the HGA.
A controller circuit board 30 suitably positions the actuator assembly 50 and then reads or writes user data in accordance with commands from a host system (not shown).
A disk drive is ultimately used to store user data in one or more xe2x80x9cdata tracksxe2x80x9d that are most commonly arranged as a plurality of concentric data tracks on the surface of its disk or disks. Special servo information is factory-recorded on at least one disk surface so that the disk drive""s servo control system may control the actuator assembly 50, via the VCM, to accurately position the transducer head to read or write user data to or from the data tracks. In operation, the disk drive""s servo control system processes (read only) the pre-recorded servo information while the disk drive processes (reads or writes) user data in the data tracks.
Earlier disk early drives used a xe2x80x9cdedicated servoxe2x80x9d system where one head and one disk surface provide the servo information for all of the other heads and disk surfaces. As shown in FIG. 2, however, the industry presently prefers an xe2x80x9cembedded servoxe2x80x9d system where the servo information is interspersed amongst the data on each surface of each disk. The factory-recorded servo information is contained in servo wedges 211 that are each divided into a plurality of servo sectors 511. The servo sectors 511 are recorded concentrically in order to provide numerous servo tracks formed from an entire rotation of servo sectors 511.
The servo information is factory recorded at the time of manufacture using a relatively expensive and low-throughput manufacturing fixture called a servo track writer (STW). The STW records the servo tracks containing the servo information on each surface of each disk for later use by the servo control system when the drive is in the hands of the user. The servo tracks are generally used throughout the life of the disk drive without modification. The operation of an STW is well known to those of ordinary skill in the art.
As shown, each servo wedge 211 generally comprises a header region HDR followed by a plurality of servo bursts (two are shown, but four is common). The header region HDR generally includes several fields (none of which are separately shown in FIG. 2) such as a setup or write splice field WRITE SPLICE, an address mark field AM, an automatic gain control/phase locked oscillator field AGC/PLO, a servo sync mark field SSM, a track identification field TKID, and a wedge number field W#. The header region HDR is followed by at least two servo bursts (an A burst and B burst are shown) that are circumferentially sequential and radially offset relative to a burst pair centerline. The servo format used is not critical and is explained here only for background purposes. The purpose of these various fields and available variations are well known to those of ordinary skill in the art.
Today, the transducer head 80 of FIG. 1 is usually provided in the form of a so-called magnetoresistive transducer that includes a separate reader and a separate writer. As the market continues to demand increased storage capacity and overall performance at reduced cost, the industry has steadily reduced the widths of the reader and writer in order to increase the track pitch and overall a real density of the disk drive. Due to normal manufacturing variations with respect to physical width, sensitivity and linearity, it has become more and more critical to characterize the reader width and writer width of individual transducers in order to optimize the capacity or performance of an individual drive and increase overall yield.
The conventional approach to characterizing the reader width is with a so-called xe2x80x9cmicro-track profilexe2x80x9d that is enabled by writing a full-width track and then erasing a portion of that track to leave a continuous, partial width characterization track 101 to the surface of the disk 23, as suggested by FIG. 3A. In developing the micro-track profile, the reader is scanned radially across the partial width characterization track 101 to produce a series of signal amplitude data points that can be analyzed with conventional techniques to establish the reader width.
The conventional approach to characterizing the writer width is with a so-called xe2x80x9cfull-track profilexe2x80x9d that is enabled by writing a continuous, full width characterization track 102 to the surface of the disk, as suggested by FIG. 3B. In developing the full-track profile, the reader is scanned radially across the full width characterization track 102 to produce a series of signal amplitude data points that can be analyzed with conventional techniques to establish the writer width.
The concepts of full-track and micro-track profiles are well known to those of ordinary skill in the art. It is also well known that the characterization takes an appreciable amount of time in the STW because the reader is successively moved to a plurality of different radial positions and, for each such position, the characterization track 101 or 102 is revolved beneath the reader for one full revolution so that the signal amplitude may be averaged over that one revolution in order to produce a track average amplitude or TAA for that particular position of the reader. The conventional process must be affected for the full-track profile and then separately affected for the micro-track profile.
FIGS. 4A and 4B are simplified illustrations of a conventional xe2x80x9csectorizationxe2x80x9d of the partial-width and full-width characterization tracks 101, 102 that provides improved accuracy in making track profile measurements. It still remains necessary, however, to take the time required to separately process the partial-width and full-width characterization tracks 101, 202.
U.S. Pat. No. 6,404,576 entitled xe2x80x9cMETHOD AND SYSTEM FOR COMPENSATION OF NONLINEARITY OR FLUCTUATION OF HEAD POSITION SIGNALxe2x80x9d (hereafter the xe2x80x9c""576 Patentxe2x80x9d), and issued Jun. 11, 2002, is an example of a method for obtaining the micro-track and full-track profiles in the field rather than in the STW. In the ""576 Patent, using multiple passes in the STW, special patterns are written in a reserved areas of the disk before shipping so that after the disk drive is in the field, the disk drive can detect a full-track profile or a micro-track profile by locating the reader at a suitable radial position while rotating these special patterns beneath the reader and taking amplitude measurements.
In the ""576 Patent, the patterns are written in the data sectors. Moreover, the pattern components are deviated from one another by being incrementally shifted radially inward across two track widths (xe2x80x9c2xc3x97Tpxe2x80x9d) in a xe2x80x9cstair stepxe2x80x9d fashion. FIG. 1 shows an example of this deviation in the context of a full-width pattern 51 used for detecting a full-track profile and FIG. 14 show an example in the context of a partial-width pattern 56 used for detecting a micro-track profile. The illustrated deviation of successive components provides patterns that are inherently xe2x80x9cscannedxe2x80x9d beneath the reader as the disk rotates since, in the field, it is impractical to accurately scan the reader over a continuous, partial or full-width track 101 or 102 like that show in FIGS. 3A and 3B as is possible while the drive is in the STW.
The ""576 Patent, in other words, is not directed to characterizing reader and writer widths while the drive is in the STW, but rather to enabling such characterizations after the drive leaves the STW. Moreover, although the pattern 51 of the ""576 Patent may be used to detect a full-track profile with one revolution of the disk and although the pattern 56 may be used to detect a micro-track profile with another revolution of the disk, many revolutions are still necessary to record such patterns 51, 56 while the disk drive is in the STW. The ""576 Patent was not directed to achieving efficiencies in the STW. Time is of the essence while drives are in the STW because they are very expensive machines that represent a significant bottleneck in the manufacturing process.
There remains a need for a disk drive with a more efficient pattern of characterization segments.
The invention may be regarded as a hard disk drive including a rotating magnetic disk and read and write elements for reading and writing data from and to the rotating magnetic disk, comprising: a magnetic characterization pattern recorded on the rotating magnetic disk for use in characterizing widths of the read and write elements using a plurality of track profiles of differing width, the magnetic characterization pattern comprising: a first plurality of characterization segments of a first radial width disposed circumferentially about a full circumference track on the rotating magnetic disk; and a second plurality of characterization segments of a second radial width that is different than the first radial width disposed circumferentially about the same full circumference track on the rotating magnetic disk.
In a more specific context, the first radial width of the first plurality of characterization segments is a fraction of the read element""s width for use in characterizing a micro track profile and the second radial width of the second plurality of characterization segments is equal to the write element""s width for use in characterizing a full track profile.
The first and second plurality of characterization segments can be arranged in a variety of locations on the full circumference track. In one embodiment, the full circumference track includes a plurality of servo sectors that each contain first and second servo burst fields and the first and second plurality of characterization segments are disposed in the servo burst fields.
The first and second plurality of characterization segments can also be arranged in a variety of desired patterns on the full circumference track. In one embodiment, the first and second plurality of characterization segments are disposed in an alternating fashion about the full circumference track on the rotating magnetic disk. In another embodiment, the first plurality of characterization segments are disposed in a first half revolution of the full circumference track and the second plurality of characterization segments are disposed in a second half revolution of the full circumference track.
The invention may also be regarded as a method of recording a pattern of characterization segments on a hard disk drive including a rotating magnetic disk and read and write elements for reading and writing data from and to the rotating magnetic disk, wherein the characterization segments are adapted for use in characterizing widths of the read and write elements, the method comprising: recording a first plurality of characterization segments that are disposed circumferentially about portions of a full circumference track on the rotating magnetic disk, the first plurality of characterization segments being of a first radial width; and recording a second plurality of characterization segments that are disposed circumferentially about other portions of the same full circumference track on the rotating magnetic disk, the second plurality of characterization segments being of a second radial width that is different than the first radial width.